I'm sure most people don't, no. The entire spectrum of healthcare, consumer goods, food production, retail (walmart anyone?), alcohol/tobacco, energy, everybody with something to gain has put money in senators' pockets at some point or another with varying degrees of regularity. There are cases across the board, from your "regular campaign donations" to senators that have been essentially installed by a single corporation or industry.

It's far more profitable to look out for the interests of the people making money off us, than to actually do right by Americans.